[meijiOrO]

Originally Posted by Plant42

Of Course there is a sort of trigger that you referred to , It's in the Twincest Arc (Novel vol.4 , Anime EP13)

Unfortunately the anime version has cut that scene off , without any reason.

The important scene that was cut.

Spoiler:

Do you remember the scene that Sydonay attack Yuuji ?
In the novel the one who rescue Yuuji is Yuuji himself , Margery comes after that.

While Sydonay try to bring Reijimaigo out of Yuuji's body , "Kaikin"(戒禁) the self defensive Jizaihou which is in Reijimaigo has triggerred.
It's cut one of Sydonay's arm which is in Yuuji's body.

After that Sydonay's arm was absorbed by Reijimaigo , and it's the key to trigger and enhance Yuuji's hidden power.
The first time he can unleashed that power is in the novel vol.7(Same scene as you see in EP18)

The only one thing I don't understand is , why they cut the Sydonay's arm scene in Ep13. May be this is the anime original adaptation ?

Spoiler:

So what is his hidden power? Is it stated in the novel already?